The corrugated paperboard industry uses flexible printing plates or dies on a rotating cylinder to transfer ink to the surface to be printed and serrated edge cutting rules on a rotating cylinder acting against a soft anvil roll to die cut the printed sheets. Such apparatus is generally called flexographic printer die cutters which apparatus, among other things, feeds individual sheets of corrugated paperboard past a rotating printing die to print indicia on the sheets and past a rotating die cylinder to die cut the sheets.
One problem associated with such machines has been the mounting of the printing die to the print cylinder, particularly, quick mounting of the printing die so as not to delay set-up of the machine during a change from one sheet size to another and/or a change in the indicia to be printed on the sheet. The printing dies themselves are usually made of a type of rubber or plastic mounted on a backing sheet of heavy paper, rubber, or plastic material. The backing sheet is flexible so that it can be wrapped around the print cylinder.
An early means of mounting the printing die to the cylinder was merely to staple the backing sheet to a wooden covering on the cylinder. This left much to be desired since the staples eventually ruined the wooden covering and the backing sheet making it necessary to recover the cylinder and, more often, to replace the backing sheet or the complete die. In addition, if the printing die was not placed properly on the cylinder, it had to be removed and repositioned thus resulting in additional set-up time.
Since then, various means have been employed to mount the printing die to the print cylinder. One such means required a rigid strip on each end of the die backing of which one was captured in an immovable slot in the print cylinder and the other captured in a movable slot. The movable slot included a hinged portion movable in a direction away from the immovable slot so as to tension the backing sheet. The hinge portion was moved by a pneumatically expandable tube. The die backing had to be made quite precisely and tube failures were not uncommon.
Another means uses a rigid U-shaped hook strip on one end of the backing sheet that hooks in a mating U-shaped slot in the print cylinder, the so-called "Dorr" system. The other end of the sheet is made similar to a roll-up window blind with the roller placed in a slot in the print cylinder. A special tool is used to wind up the roller to tension the backing sheet to hold it tightly against the cylinder. Making the backing sheet is quite complex and expensive. In addition, relatively considerable time is required to roll up the backing sheet in the cylinder.
Probably the most popular means in current use is the so-called "Matthews" system which includes a U-shaped hook strip on one end of the backing sheet that hooks in a mating U-shaped slot in the print cylinder. A number of elastic straps are fastened to the other end of the backing sheet. Each strap has a U-shaped hook that hooks into a mating U-shaped slot in the cylinder. The elastic straps tension the backing sheet tightly against the cylinder. Making the backing sheet with straps is fairly complex and expensive and some time is required to fasten each individual strap in the slot in the cylinder.
All of the above means rely on tension to hold the backing sheet tightly against the printing cylinder. However, tension is not always necessary as evidenced by the so-called "Magna Graphics" system which uses a backing sheet of ferrous material held to the cylinder by permanent magnets embedded in the cylinder's surface. Thus, both the backing sheets and the cylinder are expensive to make. In addition, any loose ferrous materials around the press are attracted to the cylinder which can damage the ink transfer roll that transfers ink to the printing die.